1. Field of the Invention
The present invention relates generally to control elements for vessels which are carried upon or within a fluid medium; and, more particularly, to fluid reaction elements and control methods for stabilizing or steering such vessels while exhibiting extremely low head loss.
2. Description of the Prior Art
Control elements of various designs and configurations are well known for stabilizing or otherwise controlling the movement of a vessel borne upon or within a fluid medium. These elements may take any of a number of physical forms and include rudders for various types of watercraft and aircraft, retractable keels for watercraft (e.g., centerboards), and large stabilizing fins for reducing roll and yaw of very large ships.
Over the years, considerable effort has been directed to the improvement of the aerodynamic or hydrodynamic designs of such vessels, but surprisingly little attention has been given to the fluid dynamics relating to the control or fluid reaction elements which are used. For example, the rudders and keels of boats, particularly sailboats, employ designs literally centuries old. The inherent deficiencies of such conventional control or fluid reaction elements limit, and thus at least partially diminish, many other recent improvements in the hydrodynamic design of various watercraft.
One of the significant problems with control elements such as rudders, stabilizers and similar devices is that they can impose quite a large drag force when used with permanent bias. Much design work has been done on sailing craft, for example, to try to reduce the drag by making the rudder smooth to the shaft or keel extension and by providing flexible rubber farings which bend as the rudder is disposed. Such structures are exemplified by the rudders disclosed in U.S. Pat. Nos. 594,068 and 3,670,685.
Such conventional rudders are not fully satisfactory since sliding or bending is required and in addition, only minor reductions in head loss or drag occur.